This invention relates to a method for increasing the productivity of olefin polymerization catalysts and to the production of such a catalyst which exhibits better productivity and produces a polymer with acceptable stereospecificity. More particularly, the invention relates to a method for washing an aluminum chloride co-crystallized titanium halide, which has been modified with an electron donor containing an ester group, with an olefin to increase the productivity of the catalyst.
U.S. Pat. No. 4,048,415, issued Sept. 13, 1977, discloses an improved process for the polymerization of olefins with a catalyst which has a titanium trichloride component prepared by reduction of titanium tetrachloride with hydrogen, silicon, metallic titanium or metallic aluminum, a complex of aluminum chloride with an electron donor, and a polysiloxane, and extracting the complex from the catalyst with a saturated hydrocarbon. We have found that better catalyst productivity can be obtained without sacrificing stereospecificity if the catalyst is washed with an olefin rather than a saturated hydrocarbon.
U.S. Pat. No. 3,404,096, issued Oct. 1, 1968, discloses a method for improving a titanium trichloride catalyst by pretreating the catalyst in an inert diluent in the absence of an activator with an olefin having 2 to 6 carbon atoms for a minimum of about 10 minutes. It is said that the catalyst undergoes a physical change whereby it agglomerates into curds and appears to swell. Defensive Publication T951,009, published Oct. 5, 1976, discloses an olefin polymerization catalyst which comprises titanium trichloride ground together with octamethylphyrophosphoramide wherein the two components are ground together in a ball mill and then contacted with proplyene for a time sufficient for from 0.1 up to 5.0 moles of propylene to be taken up by the titanium compound. Both of the above catalysts are different from the catalyst of the present invention in that they do not contain an electron donor modifier with an ester group and they both appear to react with the olefine such that material is added to the catalyst. We have found that our process provides a catalyst with better activity than the above processes and that the catalyst loses unwanted material as a result of the washing process.